The present invention relates to a method for making polyetherimides by effecting reaction between an aromatic bis(ether anhydride) and an organic diamine under solution polymerization conditions. More particularly, the present invention relates to the controlled addition of organic acid or phenol to a solution polymerization mixture for making polyetherimide.
Prior to the present invention, certain catalysts, such as sodium chloride and ferric sulfate, as shown by Williams et al, U.S. Pat. No. 3,998,840, assigned to the same assignee as the present invention, were used to enhance the rate of formation of polyetherimide under melt polymerization conditions. Although valuable results were achieved by such procedures, it was found that the aforementioned catalysts were either less effective or not effective when utilized for making polyetherimides from aromatic bis(ether anyhdride) and organic diamine under solution polymerization conditions. In addition, the presence of chloride ion may interfere with the use of such polyetherimide in electrical applications. Various metal compounds were also used to catalyze polyetherimide formation by imide-amine exchange reactions, as shown by U.S. Pat. No. 3,847,870, Takekoshi and U.S. Pat. No. 3,850,885, Takekoshi et al, assigned to the same assignee as the present invention. However, the nature of the polymerization is quite different from polyetherimide formation by the melt polymerization of aromatic bis(ether anhydride) and organic diamine, which is amine-anhydride interaction rather than imide-amine exchange.
In copending application Ser. No. 188,755, filed Sept. 19, 1980 of Tohru Takekoshi, certain oxygenated phosphorus salts were also found effective as polymerization rate enhancement catalysts for making polyimides resulting from aromatic organic dianhydride and organic diamine interaction. However, the aforementioned procedures of the prior art were based on the addition of metal salts into the polymerization mixture which resulted in the presence of metal ion residue upon the completion of such polymerization. Efforts have been made to eliminate the need for metal salt addition into organic dianhydride and organic diamine polymerization mixtures as metal ion residue often impairs the optimum properties afforded by such polyimides free of such metal ions.